1. Technical Field of the Invention
The invention is concerned with a hollow-shaft encoder with motor-shaft protective cap.
2. Prior Art
Numerous hollow-shaft encoders of this type with motor-shaft protective cap are already known from the prior art, wherein the motor shaft of a motor whose parameters, e.g., rate of revolution or position is to be determined, is led through the hollow shaft of the encoder and supported there. The inner bearing ring of the hollow shaft of the encoder is fixed on the motor shaft of the motor in a frictional and/or form-fitting manner and rotates along with it at the same rate of revolution, the outer sensor ring of the encoder remaining stationary. Due to the relative rotation of the inner bearing ring to the stationary outer sensor ring of the encoder, a measuring signal is generated that is proportional to the parameter being determined (e.g., rate of revolution or position of the motor shaft), said measuring signal being routed via an interface unit of the encoder to an external transducer and evaluation unit optionally equipped with a measuring-signal memory and display. The interface unit of the encoder, in the simplest case, is a contact strip, however, it may also already be equipped with a first internal transducer unit, or it may even incorporate an internal evaluation unit that may replace the external evaluation unit.
Especially in the case of elevator machines, the encoder is mounted at the end of the motor and the motor shaft itself passes through the hollow-shaft encoder. During rotation of the shaft the unprotected shaft presents a risk of injury. For this reason, a protective cap is installed on the encoder or over the shaft, which up to now in the prior art is being fastened with a plurality of screws. Since this shaft is used to manually move the elevator up or down in case of an outage of the machine, the protective cap must then be detached from the encoder. Detaching the cap must be performed with an appropriate tool, especially with a small wrench, which is a very tedious and time-consuming process.
With DE 39 39 868 A1, a tachogenerator for brushless motors has become known, wherein the tachogenerator is slipped with its hollow shaft over the motor shaft and frictionally connected via a conical end piece to the motor shaft. The conical end piece is connected to the motor shaft by means of a screw at the face of the free end of the motor shaft.
Various Bayonet-type connections on encoders are known, e.g., from DE 199 23 900 A1, DE 199 48 106 A1, DE 196 41 929 A1, DE 36 09 211 A1, wherein, however, the cover covering the motor shaft always incorporates essential parts of the encoder, such as, e.g., the timing disc, interface unit, or electrical connector block with optical sensor. A shortcoming lies in that a specified angle range must be adhered to for assembly purposes as the relative position between the cover covering the motor shaft and the remaining encoder, which is a hindrance particularly in the case of encoders that are difficult to reach or see, and can thus cause delays in the assembly and possibly damage to the encoder. An additional shortcoming lies in that when the axial length of the motor shaft is altered, the cover and/or remaining base of the encoder must also be altered in their axial lengths, causing significant cost disadvantages in the design, production, assembly, and warehousing.